Field of the Invention
This invention relates to a hydrostatic axial piston machine employing a bent-axis construction with a drive shaft rotatable around an axis of rotation and having a drive flange. A cylinder drum is rotatable around an axis of rotation. The cylinder drum has a plurality of piston bores that are concentric to the axis of rotation of the cylinder drum. A longitudinally displaceable piston is located in each piston bore. The pistons are fastened in an articulated manner to the drive flange. Between the drive shaft and the cylinder drum there is a driving joint in the form of a constant velocity joint for rotationally synchronous rotation of the cylinder drum and the drive shaft.
Description of Related Art
In hydrostatic axial piston machines that utilize a bent-axis construction, the longitudinally displaceable pistons located in the cylinder drum are generally fastened to the driving flange of the drive shaft by a ball-and-socket joint. The piston forces are supported via the pistons on the driving flange that is located on the drive shaft and generate a torque. In axial piston machines that utilize a bent-axis construction, during rotation there is naturally no driving of the cylinder drum with the pistons located in it. An additional device is necessary to drive the cylinder drum.
During rotation of the drive shaft, it is desirable to have the most synchronous possible driving and rotation of the cylinder drum. In the event of a non-uniform rotation of the cylinder drum, the moment of inertia of the cylinder drum with the pistons located in it would cause a non-uniform torque on the drive shaft. A non-uniform torque can result in critical stresses on the components of the axial piston machine. Undesirable noises can also occur in a drive train of which the axial piston machine is a part on account of the non-uniform torque.
To achieve a synchronous rotation of the cylinder drum and the drive shaft, on known axial piston machines that employ a bent-axis construction, constant velocity joints are used as the drive link for the rotationally synchronous drive of the cylinder drum. On known bent-axis axial piston machines, constant velocity joints that employ the Rzeppa principle are used in which roller bodies in the form of spheres (balls) that run in groove-shaped tracks in the drive flange and the cylinder drum transmit the torque between the drive shaft and the cylinder drum. Alternatively, the tripod principle is used, in which between the cylinder drum and the drive shaft there is a coupling shaft provided on both ends of the shaft with finger-like bearing pins on which are mounted the roller-shaped roller bodies that run in corresponding grooves (tracks) on the drive flange and the cylinder drum and transmit the torque to drive the cylinder drum. An axial piston machine that employs a bent-axis construction with a constant velocity joint according to the Rzeppa principle is known from DE 38 00 031 C2. Although constant velocity joints of this type that utilize the Rzeppa principle or the tripod principle result in a rotationally synchronous drive of the cylinder drum, they are difficult and expensive to manufacture on account of the complex tracks for the balls or rollers. In addition, at sufficiently high levels of torque to be transmitted to drive the cylinder drum, high Hertzian stresses occur on the roller bodies, which in constant velocity joints of this type are in the form of balls or rollers and require that the tracks be hardened to a significant depth. During the necessary hardening by a suitable heat treatment of the components provided with the tracks for the roller bodies, a change in the dimensions of the hardened components that contain the tracks occurs, which requires complicated, expensive, and time-consuming mechanical reworking operations on the hardened components. In other words, constant velocity joints that employ the Rzeppa or tripod principle require a high level of manufacturing effort and expense for the bent-axis machine.
In axial piston machines that utilize a bent-axis construction, it is known that the cylinder drum can be driven by connecting rods which are at least partly located in the piston and are connected in an articulated manner with the piston and with the drive flange by a ball-and-socket joint. The connecting rods for driving the cylinder drum are supported on the piston inside walls of the piston bores of the cylinder drum. A bent-axis axial piston machine in which the cylinder drum is driven by connecting rods is described in DE 28 05 492 C2.
Also known are bent-axis axial piston machines in which the cylinder drum is driven directly by the longitudinally displaceable pistons in the piston bores of the cylinder drum. These pistons are tapered and are provided with a tapered lateral surface. The pistons for driving the cylinder drum are supported for the drive of the cylinder drum with the tapered segments on the inside walls of the piston bores of the cylinder drum. A bent-axis axial piston machine with a drive of the cylinder drum by tapered pistons is described in DE 10 2009 005 390 A1.
In axial piston machines that utilize a bent-axis construction with drive of the cylinder drum by connecting rods or by pistons, however, on account of the limited number of pistons or connecting rods, it is not always possible to achieve an exactly rotationally synchronous drive of the cylinder drum and, thus, there is a non-uniformity of the rotational motion in the driving of the cylinder drum. A further disadvantage of bent-axis axial piston machines with a cylinder drum driven by connecting rods or pistons is that when the axial piston machine is a variable displacement machine, when the cylinder drum pivots back to a lower displacement volume, there is play between the cylinder drum and the drive shaft. The play results in an undesirable lack of synchronization between the drive shaft and the cylinder drum, which leads to an additional tangential orientation of the connecting rods or of the tapered pistons. The tangential orientation of the connecting rods or of the tapered pistons results in tangential force components that lead to a high level of reactive torque, which must be transmitted via the connecting rods or pistons, which in turn results on high stresses on the components in terms of strength and tribology.
On bent-axis axial piston machines of the type described above, an additional disadvantage is that the drive shaft cannot be routed through the axial piston machine because the constant velocity joints (according to the Rzeppa principle or according to the tripod principle) are located at the intersection of the axis of rotation of the cylinder drum with the axis of rotation of the drive shaft. Or when the cylinder drum is driven by connecting rods or by the pistons, the cylinder drum is mounted on a center pin that is located concentric to the axis of rotation of the cylinder drum. On axial piston machines that utilize the bent-axis construction with a constant velocity joint for the drive of the cylinder drum when the axial piston machine is in the form of a motor, the output of the torque, and when the axial piston machine is in the form of a pump, the drive by a torque, can occur only on one side, as a result of which the potential applications of the axial piston machine are limited. For applications of bent-axis machine in which torque is to be output on both sides or a torque for the operation of an additional consumer must be transferred through the axial piston machine, on known bent-axis axial piston machines, additional components (such as transfer cases) are necessary to make possible a universal use of the axial piston machine.
On known bent-axis axial piston machines in which a constant velocity joint that utilizes the Rzeppa principle or the tripod principle is used for the drive of the cylinder drum or in which the cylinder drum is driven by connecting rods or by the pistons, a further disadvantage is that the drive shaft equipped with the drive flange must be mounted in a cantilevered fashion in a housing of the axial piston machine. The overall length of the axial piston machine is increased by the requirement for a bearing base for the two bearings of the drive shaft.